Research in organic electronics has been gaining increasing interest in recent years due to its potential in providing low-cost fabrication, compatibility with flexible substrates, amenable to small specialized production runs, suitability for large-area deposition and suitability for mass production. Organic memory offers very attractive alternative solutions in a number of niche applications of electronics where low cost and inclusion of different functionalities are desirable. Organic memories have a simple device design, offering the potential of uncomplicated integration and simple cell concepts with very small cell sizes. They are of low-cost since they are much simpler to manufacture than silicon chips and are easy to stack, packing bits at high density. Organic memories also have the extendibility to sensing, radio frequency identification (RFID) and passive or active matrix backplanes.
Under the three main streams of semiconductor memory technologies—Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM) and Flash Memory, only the Flash memory shows non-volatile characteristics. But DRAM shows high density capabilities while SRAM has fast read/write performance. It would be advantageous to be able to combine the benefits of these three types of inorganic memories—non-volatility, high performance and high density. Organic memories offer the potential to exhibit such desired characteristics.
Although switching and memory phenomena in organic materials and devices have been reported for more than 30 years, high performance organic memory is still lacking. Three-terminal transistors, using ferroelectric polymers, and two-terminal bistable devices, which exploit charge transfer between metal atoms and organic compounds, exhibit interesting performance but are far from practical applications in memory.
A new electronic bi-stable device with a triple-layer structure consisting of two organic layers and a middle discontinuous metal layer, sandwiched between two metal electrodes, has been proposed. It exhibits promising performance and can be used as non-volatile memory. However, its fabrication is by thermal evaporation in a high vacuum, and stringent conditions are required to control the morphology of the middle, discontinuous metal layer. Additional addressing of the sandwich-type memory device and integration with other transistors is still needed. This will further increase the cost, making organic memories not cost-effective.
Floating-gate type transistor-based memory devices that utilize discrete traps as charge storage elements may be integrated as non-volatile memory in logic systems by leveraging on materials used in other silicon transistors and upon conventional silicon microelectronics know-how. The discrete charge storage elements utilized in such devices are usually isolated Si, Ge or metal nanocrystals.
Much research has been conducted on nanostructure or nano-particle formation using high temperature CMOS compatible processes. Organic memory devices which use organically passivated nanoparticles as charge storage elements can be deposited at room temperature using simple chemical self-assembly, Langmuir-Blodgett or spin-coating methods. Room temperature formation of nanostructures may find application in future 3-D organic memory architectures, compatible with the low temperature processable materials such as, for example, polymers.
Known organic memory devices involve the use of a multi-step approach of pre-synthesizing nano-particles that have a repulsive interaction so that agglomeration will not occur prior to embedding the particles in an organic layer. This is then followed by the various layers deposition process. This process is overly complex.